JPH08117816A - Method for controlling bar stripping of retract mandrel mill - Google Patents

Abstract

PURPOSE: To attain a stable operation, and to improve quality by controlling shell tension between stands in a posterior stage according to a deviation between calculated shell tension and target shell tension. CONSTITUTION: The adjusters 8 of the number of rotations and load cells 9 are mounted on the plural stands A1 to An of a retract mandrel mill. The current and the number of rotations of a motor 10 for driving mills of the stands A1 to An, are measured, and are transmitted to an arithmetic and control unit 11. The load torque of the motor 10 of a mandrel mill 1 is estimated according to the current and the number of rotations of the motor. Further, the rolling load of a stand in the posterior stage of the mandrel mill 1 is detected, and shell tension working on a shell 3 between the stands in a posterior stage is calculated from the rolling load and estimated load torque. Shell tension between the stands in the posterior stage of the mandrel mill 1 is controlled according to a deviation between calculated shell tension and target shell tension by which a stripping abnormality does not occur. Consequently, a bar stripping property can be stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling burst ripping of a retract mandrel mill for preventing a burst ripping failure after rolling of a retract mandrel mill which is a seamless pipe manufacturing machine.

[0002]

2. Description of the Related Art FIG. 2 is a schematic sectional view for explaining a rolling line in which a mandrel mill and a sizer which also serves as an extractor are arranged in series. The prior art will be described below with reference to this figure.

A hollow shell tube (hereinafter referred to as a shell) 3 perforated by a piercer is used as a mandrel bar 4 in a retract mandrel mill 1 (hereinafter referred to as a mandrel mill 1).
Stretch rolling is mainly performed by the rolling roll 6. The shell 3 stretched and rolled by the mandrel mill 1 is subjected to external diameter reduction by the sizer 2 and finished to the product size. In the rolling line of the retract mandrel mill shown in FIG. 2, the rolling by the mandrel mill 1 is completed, the averaging device 5 moves in the direction opposite to the rolling direction while the sizer 2 alone is rolling, and the mandrel bar 4 moves by the shell 3 Pulled out of.
(This is referred to as stripping.) If this stripping is not performed normally, the mandrel bar 4 moves in the direction opposite to the rolling direction by the burre retainer 5 after the completion of rolling by the mandrel mill 1. The shell 3 which is still bitten in 4 also moves at the same time and collides with the mandrel mill 1 and cannot be rolled. In order to avoid this, the following method is proposed in Japanese Patent Laid-Open No. 1-284408.

That is, the force acting on the shell 3 at the time of stripping can be known from the load of the sizer's roll 7, the number of revolutions or the electric current value of the electric motor. However, it is time-consuming to improve the stripping property. I can not afford to. Therefore, since the forces acting on the shell 3 before and after the completion of the mandrel mill rolling have a very good correlation, the stripping abnormality is detected by the shell tension before the completion of the mandrel mill rolling, and the rolling speeds of the mandrel mill and sizer are controlled. hand,
This is a method in which the shell tension during stripping is kept below the allowable limit.

[0005]

In such a conventional control method, since the mill interval between the mandrel mill and the sizer is long, the axial dimension of the shell becomes non-uniform, and the tension between the mills after rolling the mandrel mill is further increased. Or when the compressive force is removed, the clearance between the mandrel bar and the shell (clearance)
Becomes smaller and the stripping property deteriorates. In addition, a method for calculating shell tension, which is important for improving the stripping property of the mandrel bar and is closely related to the thickness and outer diameter of the shell, has not been established.

The present invention has been made in view of the above circumstances, and it is possible to easily and accurately detect the load torque of a roll of a mandrel mill, derive an accurate tension acting on the shell, and to provide a stand after the mandrel mill. Control the shell tension between them by the number of rotations of the stand roll so that the stripping abnormality of the mandrel bar does not occur.
An object of the present invention is to provide a burst ripping control method for a retract mandrel mill for stabilizing the stripping property.

[0007]

SUMMARY OF THE INVENTION The present invention is a burst ripping control method for stabilizing the burst ripping property of a retract mandrel mill, and is summarized in the following procedure.

The current and the rotation speed of the roll driving motor in the latter stage stand of the mandrel mill are detected.

The load torque of the motor of the mandrel mill is estimated based on the motor current and the rotation speed.

The rolling load of the latter stand of the mandrel mill is detected.

The shell tension acting on the shell between the latter stands of the mandrel mill is calculated from the rolling load detected above and the estimated load torque.

A deviation between the calculated shell tension and a preset shell tension that does not cause a preset stripping abnormality is calculated.

By multiplying the deviation by the control gain to correct the motor rotation speed, the shell tension between the subsequent stands of the mandrel mill is controlled.

[0014]

The burst ripping control method for the retained mandrel mill according to the present invention detects the current Ia and the rotation speed n of the roll driving motor in each stand of the mandrel mill, and based on these, the load torque T of each motor.
L is estimated by the following equation (1).

TL (s) = {K / (1 + T0.s)}. Ia (s)-{(J.s) / (1 + T0.s)}. N (s) .... (1) K: Motor field strength coefficient, Ia: Motor current, n: Motor rotation speed, J: Motor inertia moment, T0: Time constant of smoothing filter At this time, as shown in FIG. It is desirable to improve the load torque estimation accuracy of the motor by performing calculations after removing the measurement noise. Further, the rolling load of each stand of the retract mandrel mill can be measured by a load cell installed in the stand, and the coefficient of friction on the inner surface of the shell and the torque arm can be obtained in advance by experiments.

Therefore, the shell tension between the mandrel mill rear stages can be calculated from the estimated motor load torque, rolling load, shell internal friction coefficient and torque arm.

As shown in FIG. 4, there is a good (strong) correlation between the shell tension between the rear stands of the mandrel mill and the stripping force of the mandrel bar. Setting the shell tension so that it does not cause stripping abnormality, and multiplying the deviation between the target shell tension and the calculated shell tension by an appropriate gain to correct the motor speed of the rear stand of the mandrel mill. With this, the clearance between the mandrel bar and the shell is set to an appropriate value, and the stripping property of the mandrel bar is stabilized.

[0018]

FIG. 1 is a block diagram of an embodiment to which the method of the present invention is applied.

The same parts as those in FIG. 2 of the prior art are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 1, a revolving mandrel mill is newly provided with one rotation speed regulator 8 for each of the plurality of stands A1 to An, and one load cell 9 is provided for each of the plurality of stands. .

The current and the motor rotation speed of the mill driving motor 10 of each of the plurality of stands A1 to An were measured by the respective measuring instruments and transmitted to the arithmetic and control unit 11 at the same timing. In the arithmetic and control unit 11, by utilizing the correlation between the shell tension between the mandrel mill rear stand and the stripping force of the mandrel bar, the strip tension between the rear stand of the mandrel mill is controlled so that the shell tension becomes less than the allowable limit when stripping the mandrel bar. A command was issued to adjust the roll speed. Then, the shell tension between the mandrel mill latter-stage stands was estimated from the motor current and the rotation speed during the mandrel mill rolling or stripping, and the motor rotation speed of the mandrel mill was corrected so that it would be the command value.

An example of how to determine the shell tension during rolling will be described below.

The rolling torque G of each stand was determined by the equation (2).

G = ai.lambda.di.Pi- (1/2) .Ri. (Qfi-qbi) +. Mu.i.Ri.Pi ........ (2) where a is the torque arm coefficient, and λd is the torque arm. , P: rolling load, R: equivalent roll radius, qf: forward tension acting on the shell, qb:
Backward tension acting on the shell, μ: Internal friction coefficient of the shell (zero during sizer rolling), i: Stand number The left side of the above formula (2) is the load torque of the mill driving motor 10, and the following (3) It was calculated by the formula.

G = K · Ia −J · dn / dt (3) where K: motor field strength coefficient, Ia: motor current, n: motor speed, J: motor inertia Moment The above equation (3) is not directly subjected to the differential operation but is subjected to the processing for removing the measurement noise as shown in the block diagram of FIG.

Here, the first term on the right side of the equation (2) represents the first moment of the rolling load, the second term on the right side represents the torque due to the tension acting on the shell, and the third term on the right side represents the mandrel mill rolling. It represents the torque due to the frictional force between the mandrel bar and the inner surface of the shell.

The rolling load was measured by the load cell installed in each stand of the retract mandrel mill, and the coefficient of friction on the inner surface of the shell and the torque arm were also measured in advance by experiments, and the first and third terms on the right side of the equation (2) were calculated. .
Regarding the coefficient of friction on the inner surface of the shell, considering that the lubrication on the inner surface of the shell deteriorates as rolling progresses, the coefficient of friction on the inner surface of the shell is set to be larger for the latter stand. Therefore, the shell tension of the second term on the right side of the equation (2) can be calculated from the motor load torque, rolling load, shell inner surface friction coefficient, and torque arm.

The arithmetic control procedure executed by the arithmetic and control unit 11 will be described with reference to the flowchart of FIG.

(1) A target shell tension between the rear stands of the retract mandrel mill before rolling is set.

(Step-S101) (2) During rolling or stripping The motor current, motor rotation speed and rolling load are detected.

(S102-S103) The motor load torque is estimated (S104).

The shell tension between the latter stands is calculated (S105).

The control gain is multiplied so that the shell tension becomes the target shell tension, and the motor rotation speed correction amount is obtained (S106).

Burst ripping control is performed by correcting the rotational speed of the roll drive motor of each stand (S10).
7).

The control device of the present embodiment was installed in a retract mandrel mill to manufacture a steel pipe having an outer diameter of 159 mm and a wall pressure of 3 mm. The mandrel bar striking 3 to 4 out of 100 in the past. There was no ripping accident.

[0036]

As described above, according to the method of the present invention, the accurate tension acting on the shell during rolling can be detected, and the roll rotation speed of each stand of the mandrel mill can be detected based on this detected value. By controlling, the burst ripping property can be stabilized. Therefore, in the production of seamless pipe, it exerts a great effect on stable operation and quality improvement.

[Brief description of drawings]

FIG. 1 is a device configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a sizer that also serves as a retract mandrel mill and an extractor.

FIG. 3 is a block diagram showing an example of calculation of motor load torque according to the method of the present invention.

FIG. 4 is an explanatory diagram showing the relationship between the shell tension between the mandrel mill rear-stage stands and the shell tension during burst ripping.

FIG. 5 is a flowchart showing a process of burst ripping control of the mandrel mill.

[Explanation of symbols]

 1 Mandrel mill 2 Sizer 3 Shell 4 Mandrel bar 5 Bar retainer 6 Mandrel mill roll 7 Sizer roll 8 Rotation speed regulator 9 Load cell 10 Mill drive motor 11 Computational control unit

Claims (1)

[Claims] 1. A method for controlling burst ripping of a retract mandrel mill having an extractor for burst ripping or a sizer also serving as an extractor on the output side, wherein the current and the rotational speed of a roll driving motor in a stand after the mandrel mill are adjusted. Detecting, estimating the load torque of the motor of the mandrel mill based on the motor current and the number of revolutions, further detecting the rolling load of the mandrel mill rear stand, from the rolling load and the estimated load torque the mandrel mill rear stand It is characterized in that the shell tension acting on the shell between is calculated, and the shell tension between the subsequent stands of the mandrel mill is controlled based on the deviation between the calculated shell tension and the target shell tension that does not cause stripping abnormality. Retract mandlermi Burst ripping control method of.